Traffic in Rio de Janeiro, Brazil. Yasuyoshi Chiba/Getty Images Navigation company TomTom has published a list of the most congested cities in the world.

The TomTom Traffic Index, posted online on Tuesday, is based on 19 trillion data points collected over nine years from 390 cities, according to the Dutch company.

Each city's congestion level was given a percentage score out of 100, with levels ranging from 66% in the most congested cities to 9% in the least.

TomTom defined the congestion level as the "increase in overall traffic times when compared to a free flow situation (an uncongested situation)."

Ralf-Peter Schaefer, VP TomTom Traffic, said in a statement that the traffic index is "designed to help drivers, cities and transport planners to understand traffic congestion and, most importantly, how to reduce it."

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